Alkylation process



United States Patent Delaware No Drawing. Filed Aug. 20, 1963, Ser. No. 303,409 6 Claims. (Cl. 260-624) This application is a continuation-in-part of co-pending application Serial No. 33,902, filed June 6, 1960, now US. Patent No. 3,116,336, issued December 31, 1963.

This invention relates to the production of ortho-alkylsubstituted phenols. More particularly, it relates to a process for selectively ortho-alkylating phenol and to novel catalysts which are employed in the process.

The presence of the hydroxyl group on the benzene ring in phenol tends to control substitution on the ring in such a manner that substitution takes place on the ring carbon atoms ortho and para to the hydroxyl group. In phenol, the activating influence of the hydroxyl group renders the ortho and para ring positions active, but to different degrees and in general, the para position is the more active. For example, it is well known that in the conventional Friedel-Crafts alkylation phenol is monoalkylated primarily in the para position and the subsequent dialkylphenol is the 2,4-disubstituted product. Furthermore, the conventional Friedel-Crafts alkylation of phenol produces mixtures of products wherein the predominant compounds are the 4-alkyl-, 2,4-dialkyland 2,4,6-trialkylphenol.

Substituted alkylphenols have considerable industrial utility because of their antioxidant properties. Probably the most useful compounds of this type are the 2,6-dialkylphenols, particularly those 2,6-dialkylphenols wherein at least one of the alkyl substituents is branched on the alpha carbon atom, e.g., Z-methyl-6-tert-butylphenol, 2,6-diisopropylphenol and 2,6-di-tert-butylphenol. While such compounds are presently of considerable commercial importance, they have been expensive when produced by conventional alkylation processes, because of their production in undesirably small quantities and the presence of the desired products as components in mixtures with major amounts of para-alkylated phenol derivatives. Furthermore, these conventional processes are complicated by the formation of such by-products as the isomeric others, the formation of which reduces the yield of desired product and renders product recovery more difficult.

It is an object of this invention to provide a process for selectively ortho-alkylating phenol. A further object of the invention is to provide a process for the selective diortho-alkylation of phenol which can be conducted under moderate conditions of temperature and pressure and which employs certain relatively inexpensive but effective sulfur-containing catalysts. The provision of such a process for providing high yields of di-ortho-alkylated phenol in comparably short reaction time is an additional object.

It has now been found that these objects are accomplished by the process of selectively di-ortho-alkylating phenol by reacting an olefin and phenol, the olefin/ phenol ratio being at least about 2:1, at a temperature of at least 100 C., in the presence of a catalytic amount of a sulfonic acid selected from the group consisting of alkanesulfonic acid, benzenesulfonic acid, 3,6-dihydroxy-1,4- benzenesulfonie acid and naphthalenesulfonic acid.

3,177,259 Patented Apr. 6, 1965 By conducting the process of the invention under these conditions it has been unexpectedly found that the principal reaction product is a di-ortho-alkylated phenol, and substantial para-alkylation of the aromatic ring occurs only after both ortho positions have been alkylated. This discovery is, of course, surprising in view of the extensive showing in the art that when sulfuric acid is employed to catalyze the alkylation of phenol with olefin, the first and principal product is 4-alkylphenol', the ortho positions being difficult to alkylate even after the para position has been alkylated.

The olefinic reactants which are employed to orthoalkylate phenol are the unsaturated hydrocarbons having one or more double bonds. Preferred olefins are those compounds having up to two olefinic, i.e., non-aromatic, carbon-carbon double bonds and from 2 to :20 carbon atoms. The olefins may be acyclic, e.g., ethylene, propylene, butylene, isobutylene, butadiene, amylene, hexylene, isoprene, dodecene, eicosene and the like, or they may be cyclic olefins such as cyclopentene and cyclohexene. The olefins may be wholly aliphatic or may have aromatic substituents, as exemplified by styrene, alphamethylstyrene, divinylbenzene, allylbenzene or the like. Of these olefins, the most preferred class, and that which afiords dialkylphenols having the most desirable properties, are the monoolefins having from 2 to 8 carbon atoms, particularly those monolefins having from 3 to 5 carbon atoms, e.g., propylene, butylene, isobutylene, amylene and isoamylene, these olefins being the most reactive under the conditions of the process.

The selective nature of the process is obtained when the olefin is employed in amounts equivalent to or in excess over the phenol. Thus, in the selective di-ortho-alkylation process of the invention, at least two moles of olefin per mole of phenol have been found to be necessary, and molar amounts of at least three moles of olefin per mole of phenol are preferred. The use of more than about six moles of olefin per mole of phenol, however, tends to unnecessarily dilute the reaction system and increase the reaction time, and is therefore uneconomical. Because of the desirability of conducting the alkylation in the presence of an excess of olefin, it is preferred to bring the reactants together very quickly, as by charging the gaseous or liquid olefin to the phenol in a short time so that an excess of the olefin is present in the reaction zone during reaction. Alternatively, the phenol may be charged to a reaction zone already containing the olefin reactant.

The phenol and olefin are reacted under particular alkylating conditions to yield the desired di-ortho-alkylphenols. It has been found that the selectivity of the process is a result of the conditions employed as well as of the catalyst utilized. The reaction conditions, i.e., concentration of reactants, reaction temperature and reaction pressure are therefore of great significance in determining the distribution of alkylated phenolic products obtained.

The selective di-ortho-alkylation takes place at temperatures of at least C., but below about 250 C. At lower temperatures, the reaction rate tends to be undesirably low, while at higher temperatures dealkylation and rearrangement of products takes place at a competitive rate. Preferred reaction temperatures are substantially higher than 100 C., e.g., at least about C., and best results are obtained when the selective diortho-alkylation is conducted at temperatures from about C. to about 200 C.

For many of the olefinic reactants, the alkylation proceeds at a desirable rate at these temperatures when the process is conducted at atmospheric pressure, although the use of pressures greater than atmospheric is advantageous when olefins which are gases at reaction temperature are employed, particularly such lower olefins as ethylene, propylene, isobutylene and cyclohexene. In general, it is preferred to conduct the alkylation at pressures above atmospheric. This may be accomplished by conducting the alkylation in a sealed reactor, so that the sum of the partial pressures of the reactants therein is greater than atmospheric when at reaction temperature. Alternatively, the reaction zone may be pressurized with an excess of the reactant olefin or with a gas inert under reaction conditions such as nitrogen, carbon dioxide, argon or helium. The pressure required is that sufiicientto maintain the reactants in the liquid phase, and therefore will be dependent upon the particular olefin employed. Conveniently, superatmospheric pressures greater than about 100 p.s.i.g. are employed. As pressures from about 100 p.s.i.g. to about 3000 p.s.i.g. may be obtained in conventional equipment, these pressures are preferred.

The reaction is conducted under non-ionic, substantially anhydrous conditions. While traces of water, such as are normally present in the reactants and catalyst, can be tolerated, it is desirable to keep the total concentration of water in the reaction system below about Water by weight and preferably below about 1% by weight. Therefore special predrying of reactants and catalyst is not required although reasonable precautions should be taken to avoid the introduction or buildup of water in the reaction equipment.

At least as important as the selection of the noted reaction conditions is the use of the particular sulfonic acids which have been found to catalyze the selective di-orthoalkylation under these conditions. The catalyst is selected from the group of sulfonic acids consisting of alkanesulfonic acid, benzenesulfonic acid, 3,6-dihydroxy-l,4-benzenedisulfonic acid and naphthalenesulfonic acid. Of these catalysts, the alkanesulfonic acids are preferred, and the most preferred catalyst is methanesulfonic acid. These catalysts are all realtively inexpensive compounds which are commercially available, and when employed in catalytic amounts are sufiiciently non-corrosive as not to require special glassor stainless steel-lined reaction equipment.

The alkanesulfonic acid catalysts of the invention have the formula RSO H wherein R is an alkyl radical, preferably having up to 4 carbon atoms. Representative compounds are methanesulfonic acid, ethanesulfonic acid, propanesulfonic acid and butanesulfonic acid. These compounds are difficult to maintain in the anhydrous state, and are generally obtained and employed in the hydrated form. Other sulfonic acids found to direct the selective di-ortho-alkylation of the invention are the arylsulfonic acids selected from the group consisting of benzenesulfonic acid, 3,6-dihydroxy-1,4-benzenedisulfonic acid and naphthalenesulfonic acid. Either alphaor betanaphthalenesulfonic acid is suitable. It has been found that while these enumerated compounds have superior ortho-directing properties, their alkyl-substituted homologs do not. For example, while benzenesulfonic acid is an excellent catalyst under the conditions of the reaction, p-toluenesulfonic acid does not exhibit the property of selectively catalyzing di-ortho-alkylation.

It has been observed that only catalytic amounts of these sulfonic acids are required. The optimum amount of catalyst required in a particular reaction will, of course, be dependent upon the reaction conditions as well as the particular catalyst employed. At higher temperatures, for example, somewhat smaller amounts of catalyst are required than at lower temperatures. Generally, the amount of sulfonic acid catalyst employed should be between about 0.001 mole and about 0.1 mole per mole of phenol, with amounts from about 0.005 mole to about 0.05 mole per mole of phenol being preferred. This comparatively small amount of catalyst that is required is, of course, one of the advantages of the invention in that the product is easily purified of these amounts. The catalyst is conveniently introduced into the reaction zone by pre mixing it with the phenol. In general, all the catalysts are liquids or low melting solids which are readily mixed With the phenol and the resulting mixture charged to the reaction zone. When the process is conducted in accordance with the above description, the reaction takes place in short times, generally from about 0.25 to about 2 hours.

The reaction may be conducted in a batchwisc manner, preferably by adding the phenol reactant containing the catalyst to a reactor and rapidly passing in the olefinic reactant under conditions where maximum mixing of the reactants is achieved. As the olefinic alkylating agents are generally gases or liquids under reaction conditions, they can be added to the heated phenol-catalyst mixture as fast as they can be absorbed. Alternatively, the reaction may be conducted in a continuous manner, as by passing streams containing the catalyst and reactants through a reaction zone where they are subjected to the necessary conditions of mixing, heat and pressure for a time sulficient to produce the desired 2,6-dialkylphenol in suitable yield. The unreacted phenol and olefin are readily recovered and recycled to the beginning of the reaction zone and the alkylated by-products can be recovered, dealkylated, recycled or otherwise employed.

As the di-ortho-alkylated phenols may react further with olefin to form undesirable 2,4,6-trialkylphenol, it is customarily desired to stop the reaction before completion, e.g., when the relative amount of 2,6-dialkyl phenol is at a maximum. The reaction is stopped at any desired time by such conventional means as cooling, separating the reactants or neutralizing the catalyst. The latter is easily accomplished by adding aqueous caustic to the system, thus both cooling the system and neutralizing the catalyst, thereby preventing isomerization, transalkylation and disproportionation.

The reaction products are separated at the termination of the process by such well known methods as fractional distillation, selective extraction, as with caustic, and sim ilar methods. The 2,6-dialkylphenol so recovered may be used as an antioxidant, or as an intermediate in the production of other antioxidants or other useful materials. Typical products obtained by the process of the invention include 2,6-diethylphenol from phenol and ethylene, 2,6- di-tert-butylphenol from phenol and isobutylene, and 2,6- dicyclohexylphenol from phenol and cyclohexene.

To further illustrate the process of the invention, the following examples are provided. It should be understood that they are not to be regarded as limitations, as the teachings thereof may be varied as will be understood by one skilled in this art.

EXAMPLES The following experiments were conducted in a one liter stainless steel horizontal stirred autoclave employing phenol and isobutylene as reactants. The isobutylene was very pure, on the order of 99+%, and was prepared by catalytic dehydration of tertiary butyl alcohol. Analytical grade phenol containing about 0.5% Wt. water and 0.15% H PO (as preservative) was employed. The candidate catalysts were first dissolved in molten phenol and the mixture was charged to the reactor and warmed to 150 C. with stirring. Liquid isobutylene was charged under pressure to the reactor during a 10-20 second period, and the reaction temperature was maintained at about 150 C. during the course of the reaction.

During the course of the reaction, small samples were withdrawn from the reactor and analyzed by gas-liquid chromatography on a 2.5 meter x 6 mm. glass column packed with -100 mesh Chromasorb W impregnated with 20% DC-710 silicon oil which was operated at 197 C. with a helium flow of 60 cc./min.

Examples 1-8, conducted in this manner are set forth in Table l.

about 200 C., and a pressure of at least about 100 p.s.i.g., in the presence of from about 0.001 to about 0.1 mole per Table 1 Charge Composition of Alkylate,

Mole Percent Alkylation Alkylation Example Catalyst Temp, C. Time, Min.

Moles Iso- Moles Moles t-Butyl Butylene Phenol Catalyst Phenol Ether of Phenol N ne 3. 0 1. 0 150 100.0 Mcthanesulfonic acid 3. 21 1. 0 0. 008 150 60 11. 1 5. 2

3, 6-dil1ydroxy-1, 4-benzene ionic acid 3. 34 1. 0 0. 005 150 90 18. 1 7. 4 Naphthalene beta-sulionic acid. 3. 0 1. 0 0. 01 150 17 8. 8 3. l Benzene-sulfom'c acid 3. O 1. 0 0. 01 150 4. 7 7. 1 98% H 504 3. 0 1.0 0. 005 150 60 10. 4 2.0 p-Toluene-sultonic acid 3. 0 1. 0 0. 02 150 16 13. 0 4. 1 65% H SO4 3. 0 1. 0 0.00064 150 64 64. 1 22. 4

Composition of Alkylate, Mole Percent Example Catalyst t-Butyl Percent 2-tButyl 4-t-Butyl Ether of 2, G-Di-t- 2, 4-Di-t- 2, 4, G-Tri- Yield of Phenol Phenol 2-t-Butyl Butyl Butyl t-Butyl 2, 6,-Di-t- Phenol Phenol Phenol Phenol Butyl Phenol None Methane-sulfonic acid 23. 7 9 8 35. 6 6. 4 16. 4 3, 6-dihydroxy-1, 4-benzene- 23.8 2. 1 l. 3 28.6 5.8 12. 9

disulfonie acid. Naphthalene beta-sulfonic acid. 23. 7 2. 1 9 31. 0 10.9 19. 5 Benzene-sulfonic acid 24. 3 2. 1 2. 4 29. 6 11. 6 18. 4 98% H 804 23. 0 3. 7 1. l 24. 5 14. 2 21. 2 p-Toluene-sulfonic acid. 15. 8 2. 5 5 12. 6 33. 0 18.6 65% H2804 l0. 2 1. 5 1. 1 5 1 0 I claim as my invention:

1. The process for selectively di-ortho-alkylating phenol by reacting under substantially anhydrous conditions an olefin and phenol, the olefin/phenol molar ratio being at least 2:1, at a temperature of at least 100 C. but below about 250 C. in the presence of from about 0.001 to about 0.1 mole per mole of phenol of a sulfonic acid selected from the group consisting of alkane-sulfonic acid wherein the alkane moiety has up to 4 carbon atoms, benzenesulfonic acid, 3,6-dihydroxy-1,4-benzenedisulfonic acid and naphthalenesulfonic acid.

2. The process for selectively diortho-alkylating phenol by reacting under substantially anhydrous conditions an olefin and phenol, the olefin/phenol molar ratio being at least about 2:1, at a temperature of at least 100 C. but below 'ab6ti't250" C. and a pressure sufiicient to maintain the reactants in liquid form, in the presence of from 0.001 to about 0.1 mole per mole of phenol of a sulfonic acid selected from the group consisting of alkane-sulfonic acid wherein the alkane moiety has up to 4 carbon atoms, benzenesulfonic acid, 3,6-dihydr0xy-1,4-benzenedisulfonic acid and naphthalenesulfonic acid.

3. The process for selectively di-ortho-alkylating phenol by reacting under substantially anhydrous conditions an olefin and phenol, the olefin/phenol molar ratio :being at least about 2:1, at a temperature from about 120 C. to

mole of phenol of a sulfonic acid selected from the group consisting of alkanesulfonic acid wherein the alkane moiety has up to 4 carbon atoms, benzenesulfonic acid, 3,6-dihydroxy-l,4-benzenedisulfonic acid and naphthalenesulfonic acid.

4. The process of claim 3 wherein the olefin is a monoolefin having from 3 to 5 carbon atoms.

5. The process of claim 4 wherein the olefin is isobutylene.

6. The process for selectively di-orth0-alkylating phenol by reacting under substantially anhydrous conditions phenol and isobutylene, the isobutylene/ phenol molar ratio being at least about 2:1, at a temperature substantially higher than C. but below about 250 C., and a pressure of at least about 100 p.s.i.g., in the presence of from about 0.001to about 0.1 mole per mole of phenol of methanesulfonic acid.

References Cited by the Examiner UNITED STATES PATENTS 2,014,766 9/35 Isham 260-624 X 3,082,258 3/63 McConnell et a1 260-624 LEON ZITVER, Primary Examiner.

HAROLD G. MOORE, Examiner. 

1. THE PROCESS FOR SELECTIVELY DI-ORTHO-ALKYLATING PHENOL BY REACTING UNDER SUBSTANTIALLY ANHYDROUS CONDITIONS AN OLEFIN AND PHENOL, THE OLEFIN/PHENOL MOLAR RATIO BEING AT LEAST 2:1, AT A TEMPERATURE OF AT LEAST 100*C. BUT BELOW ABOUT 250*C. IN THE PRESENCE OF FROM ABOUT 0.001 TO ABOUT 0.1 MOLE PER MOLE OF PHENOL OF A SULFONIC ACID SELECTED FROM THE GROUP CONSISTING OF ALKANE-SULFONIC ACID WHEREIN THE ALKANE MOIETY HAS UP TO 4 CARBON ATOMS, BENZENESULFONIC ACID, 3,6-DIHYDROXY-1,4-BENZENEDISULFONIC ACID AND NAPHTHALENESULFONIC ACID. 